The present invention relates generally to brake pads and to brake calipers, particularly for heavy commercial vehicles, such as lorries, trucks and trailer units for lorries and trucks.
Known brake arrangements include a brake carrier fixed to a suspension component of a vehicle and a slideably mounted caliper having a pair of brake pads, between which sits a brake rotor (brake disc). An actuator, generally mounted on an inboard side (also known as an actuator side) of the caliper, is capable of forcing the inboard pad (also known as an actuator side pad) towards the brake rotor. A caliper frame is slideably mounted on pins or the like. A reaction force causes the caliper frame to slide inboard as the inboard pad moves towards the brake rotor. This causes an outboard portion (also known as a reaction side portion) of the caliper frame to force the outboard pad (also known as a reaction side pad) to contact and brake the brake rotor in conjunction with the inboard pad. The brake rotor itself is axially fixed.
Pad abutments prevent the brake pads from rotating with the brake rotor during braking. Typically, the pad abutments engage corresponding carrier abutments of the brake carrier. Thus, the caliper frame slides relative to the brake carrier, and the brake carrier is axially fixed relative to the brake rotor. Hence, the carrier abutments are axially fixed relative to the brake rotor.
Typically, each brake pad includes a steel brake pad backplate to which friction material is secured. Braking torque is transferred from the friction material, to the brake pad backplate, to the pad abutment, and then to the carrier abutment.
As the friction material on the inboard brake pad wears, the inboard brake pad backplate advances towards the axially fixed brake rotor. Similarly, as the friction material on the outboard brake pad wears, the outboard brake pad backplate advances towards the axially fixed brake rotor.
The above design is known as a sliding caliper brake, an example of which is described in Japanese Patent Application 7-139570. Fixed caliper/sliding rotor brakes are also known. In such a brake, the caliper is fixed relative to a suspension component of the vehicle and includes caliper abutments that the brake pad abutments react against. The brake rotor includes splines to allow movement relative to the brake caliper when the brakes are applied. Therefore, the brake rotor moves relative to the caliper abutments. Such a moveable caliper is disclosed in European Patent Application 1074757.
As the frictional material of brake pads on a fixed caliper/sliding rotor brake wear, the movement of the brake pads and the brake rotor is significantly different to the movement of the brake pads and the brake rotor when the friction material of a sliding caliper brake wears. Thus, when the friction material of the reaction side pad of the fixed caliper/sliding rotor brake wears, the reaction side brake pad backplate remains stationary. Hence, the sliding rotor advances towards the reaction side brake pad backplate. This requires the actuator side brake pad to also move towards the reaction side brake pad to maintain a correct running clearance between the actuator side brake pad and the brake rotor. This movement results from wear on the reaction side brake pad friction material. When the actuator side brake pad friction material wears, the actuator side brake pad backplate must advance towards the brake rotor to maintain a correct running clearance between the friction material and the brake rotor. For example, assuming that the friction material on the actuator and reaction side brake pads wear at the same rate, for every one millimeter of wear of the friction material on the actuator and reaction side brake pads, the brake rotor must advance towards the reaction side brake pad backplate by 1 millimeter. The actuator side brake pad backplate must, however, advance towards the reaction side brake pad backplate by two millimeters i.e., the total wear on both the brake pads. Thus, the actuator side brake pad backplate on a fixed caliper/sliding rotor brake moves twice as far as the equivalent actuator side brake pad backplate on a sliding caliper brake. This means that the caliper abutments that the actuator side brake pad abuts against on a fixed caliper/sliding rotor brake must accommodate twice as much movement of the actuator side brake pad as an equivalent sliding caliper brake. This causes significant problems in the design and packaging of a suitable caliper and pad abutment for the actuator side brake pad of a fixed caliper/sliding rotor brake.